First thing is to determine a common technology that your pc, pda, and phone all share. If they all can display webpages then you have several options. If not, possibly java as its on most cell phones these days and I believe PDA's have supported java for awhile now. But in that case, the java application would have to be installed on each device.

Thanks Phaelax for your reply to my post

Basically i am going to use 3 tier architecture. User interface processing engine, and a backend database.

the user interface will be a web portal, processing engine will be j2ee, and the backend will be oracle DB2 or my sql.

The pc mobile phones and pda will all have to be able to play and read mp3 files it is aimed at people who have access to the web through these devices it is not my proect to install a java application on each device. (is this a good decision choice)

also I want to know how to devise my plan for it and what i would include, Ive got to give in my plan this week coming.

thanks Brims

i know this is seriously late

so you want to store the mp3's in the database? why not just use the database to link to them so
user interface (html with serverside scripting) - database - files dumped into a folder

that way you can have various user interfaces and almost no performance issues on the db. most phones and pdas can browsw html